The invention generally relates to optical communication systems) and more particularly, to a Comb Wavelength Division Multiplexer for optical communications.
As optical telecommunication technology develops, information transmitted through optical fiber expands, and the full optical network grows, higher requirements are set for technologies like DWDM, optical passive devices. At present time, DWDM is implemented with grating, light waveguide, interference filter, birefringent filter and the like, but since density of channel are getting denser and denser, a better device is needed to multiplex or demultiplex signal. For example, DWDM may use the wavelength division device with birefringent crystal filter. Current design adopts one-stage filter to reduce the size of the device, but channel separation is poor. However, if two birefringent crystal filter element groups are applied to improve performance, the construction of two-stage filter is very complicated and the cost is expensive.
The invention overcomes above-mentioned problems with a new wavelength division device. A purpose of the invention is to obtain a two-stage filter effect with only one group of birefringent filters by light reflection The device has a reduced size and a better channel separation.
According to one aspect of the invention, a reflective parallel light polarization splitter 6 of the comb wavelength division multiplexer comprises a polarization splitter 6-1 and a right-angle prism 6-2, a slant side of the right-angle prism is parallel to a surface of the polarization splitter.
According to another aspect of the invention, a reflective parallel light polarization splitter 6 of the comb wavelength division multiplexer comprises a xcex/2 phase delay wave plate 6-3, 6-4 disposed symmetrically in front of a polarization splitter 6-1, a xcex/4 phase delay wave plate 6-5, and a flat mirror 6-2.
One feature of the above-mentioned comb wavelength division multiplexer is an I/O device comprising a three-core collimator and trapezoid prism, or comprising a three-collimator array.
Another feature of the above-mentioned comb wavelength division multiplexer is that a PMD compensator 3 be disposed between the polarization splitter 2 and the xcex/4 phase delay wave plate device.
One advantage of the invention is duplicative use of a birefringent crystal filter element group by reflection to attain a dual-stage filtering effect, the channel isolation degree is greater than one-stage filter, the number of elements is lesser and package size is smaller. The second advantage is that the construction is independent on the polarization of input light. The third advantage is that the construction provides PMD compensation and eliminate PMD effect of device on the system. A device of wavelength division multiplexer of the invention can couple DWDM signals of odd channel and even channel into different fibers, so that the channel spacing is doubled and the signals are demultiplexed. The device can also couple signals of two channels into one fiber to realize multiplexing. If changing the birefringent filter in the device, we may also obtain devices like optical attenuator, optical modulator and optical 1xc3x972 switcher with high isolation degree.
The invention provides a comb wavelength division multiplexer, comprising: an input device at input side; a polarization splitter; a xcex/2 phase delay wave plate; a birefringent crystal filter; and a reflective parallel light polarization splitter for reflecting an incident light beam from the birefringent crystal filter into the birefringent crystal filter again, and passing the reflected light beam through the xcex/2 phase delay wave plate and the polarization splitter to an output side, so that the input side and the output side are a same side;
The invention still provides a comb wavelength division multiplexer, comprising: an input device at input side, a polarization splitter; a xcex/2 phase delay wave plate; a birefringent crystal filter; a mirror; a xcex/4 phase delay wave plate; a polarization splitter; and two xcex/2 phase delay wave plates, said two xcex/2 phase delay wave plates are disposed respectively in an reflective optical path in front of the polarization splitter: said xcex/4 phase delay wave plate is disposed between the polarization splitter and the mirror.